Launch Viber (minimized) at startup

Launch the application preferences manager at startup:

gnome-session-properties

Then add a Viber item with the following command:

Name: Viber
Command: /opt/viber/Viber StartMinimized
Comment: Commentaire par défaut.

To launch Skype with a specific user (to launch it minimized, options->Start Skype minimized in the system tray):

Name: Skype
Command: /bin/sh -c  "echo 'tbourdin.partitech xxxxx' | skype --pipelogin"
Comment: Skype.

Version context

This procedure describes the software and the environment available at the time of its publication. The packages, interfaces, and repositories mentioned may have changed or disappeared; first check the system version and its support level.

cat /etc/os-release
uname -r

Work on a backup or a snapshot, note every modified file, and prepare for rollback. For a current workstation or server, prefer signed packages from officially supported repositories.

Reference: official Ubuntu lifecycle.